Numerous apparatuses are already known in industry, and in particular in the automotive industry, for depositing paint on objects, in particular on motor vehicle bodywork.
In general, vehicles are "recognized" by computer means for their finishing colors.
In practice, various projection devices are used, in particular electrostatic projection devices which may include bowl-shaped rotating head systems. Such devices may be coupled to an automatic color changer. This assembly then allows the complete unit to change vehicle color. Further, before applying the final color to a vehicle, i.e. the finishing color, a primer or sealer which is generally a single gray color is applied in the great majority of cases. However, for some finishing colors, and in particular yellows and reds, are known for their lower opacifying power, gray primer is unsatisfactory and thus contributes to considerably increasing the return rate for defects.
The use of "false color" primers, i.e. primers of color similar to the finishing color, in order to facilitate the industrial use of finishing colors of low opacifying power on a mass production line has suffered, heretofore, from several drawbacks.
A given production site works, on average, with a palette of 15 to 20 different colors. Thus, in order to avoid excessively complicating management and equipment, it would seem reasonable to provide for 3, 4, or 5 "false color" primers.
However, present installations are generally not suitable for setting up one or more additional paint circuits or paths, and the cost of adding such paint circuits as would be necessary for using new primer colors in a production line has often been judged to be much too high.
Even in a new installation, the extract cost resulting from such a choice is phohibitive both because of the extra equipment that needs to be installed and also because of requisite materials need storage, and in addition, it has been observed that even when 3, 4, or 5 "false color" primers are available it is still not possible to adapt the color of the primer adequately to some finishing colors so that there is still a return rate due to defects which is unacceptable, in particular when taking account of the extra production costs resulting from the presence of a plurality of primers and paint circuits.
The present invention thus seeks to solve the new technical problem consisting in providing a solution for simplifying primer technology by virtue of using a single primer which requires only one main paint circuit and which is capable of being adapted at will on site to an appropriate primer color as a function of any given finishing color.
The invention also seeks to solve the complementary technical problem concerning the losses of material related to purging operations when changing color as are required by color changes such as those used for finishing colors.
The present invention also seeks to solve the technical problem consisting in providing a method and an apparatus enabling investment costs to be kept down.
All of these technical problems are solved for the first time in satisfactory manner by the present invention.